To "bottom out" is when one is having sex and the penis reaches the cervix, or the top part of the vagina, and can go no deeper. This can be referred to as "bottoming out," or in the past tense as "bottomed out."

It can be either painful or pleasurable, depending on the girl and how extreme the bottoming out is.

Man, I was fucking this chick last night and she told me to stop cause my dick was so big I was bottoming out on her.

The Urban Dictionary Mug

Having sex with a group of people then asking for them to knock you out by any method, preferable by a punch or punches to the face. After you are knocked out then the group proceeds to have sex with your unconscious body.